Slack adjuster for railway car brakes



June 30, 1970 F. P. ADLER 3,517,786

SLACK ADJUSTER FOR RAILWAY CAR BRAKES Filed Feb. 23, 1968 3 Sheets-Sheet 1 F I E11 2 f7 J4 J9 154 Q f J6 J5 J5 Q Q 29 20 J Fr] F. P. ADLER SLACK ADJUSTER FOR RAILWAY CAR BRAKES June 30, 1970 I5 Sheets-Sheet 2 Filed Feb. 23, 1968 June 30, 1970 F. P. ADLER 3,517,736

SLACK ADJUSTER FOR RAILWAY CAR BRAKES Filed Feb. 23, 1968 v 5 Sheets-Sheet :5

- \z Flt-3.5 1Q 39 United States Patent 3,517,786 SLACK ADJUSTER FOR RAILWAY CAR BRAKES Franklin P. Adler, 105 Boyd Circle, Michigan City, Ind. 46360 Filed Feb. 23, 1968, Ser. No. 707,542 Int. Cl. F16d 65/54 US. Cl. 188-200 13 Claims ABSTRACT OF THE DISCLOSURE The brake actuating mechanism and slack adjuster include a dead body lever, a piston actuated live body lever and a dead take-up lever. The piston is also connected to the take-up lever by an overthrow device. A telescopic center rod includes a rack connected to the dead lever, and a pawl connected to the live lever and normally maintained out of engagement with the rack by a control rod connected to a sensing lever. A cable and pulley arrangement, connected at one end to the takeup lever, draws the two body levers toward each other, when the piston is extended, with a mechanical advantage less than that developed by the live lever system. This causes as much as 60 inches of slack to be taken up by less than 7 /2 inches of piston movement. The sensing lever, pivoted at one end to the live lever, senses extension of the piston beyond 7 /2 inches and causes engagement of the pawl with the rack. Further movement of the piston develops a braking force of high mechanical advantage through the locked telescopic center rod. The overthrow device absorbs piston movement after all slack is taken up.

This invention relates to slack adjusters for the brake rigging of railway cars.

The slack in the brake rigging of railway cars includes not only the brake shoe clearance with respect to the wheel but also the play in all of the various link connections, with the result that the total amount of slack in the brake rigging is much greater than that which can be taken up by the amount of piston travel available, which is 12" when a 10 x 12 type brake cylinder is used.

A slack adjuster is a device which regulates the amount of slack in the system to produce a set amount of piston travel. Too small an amount of piston travel produces high cylinder pressure with the danger of slid flat wheels, and long piston travel reduces the braking force, while excessive slack, which is beyond the 12" travel of the brake cylinder, results in no braking force at all.

An object of my invention is to provide a slack adjuster which has much greater take-up capacity than the prior art arrangements.

Another object is to provide a slack adjuster which returns all of the slack to the rigging at the conclusion of each braking operation. This eliminates any possibility that the brake shoe will remain in contact with the wheel after the braking pressure is released. Another advantage is that there is sufficient clearance between the brake shoe and the wheel so that any number of brake shoes can always be replaced without adjusting the slack adjuster.

Prior art slack adjusters regulate the slack in the sense that when the brakes are released, enough slack is returned to the system to accommodate 7 /2 inches of piston travel. Under the relatively high mechanical advantage built into the brake actuating mechanism, this built in slack is not sufiicient to permit the replacement of more than one or two brake shoes, although it often happens that three or more replacement shoes are required.

Three or more brake shoes can be replaced if, after the replacement of the one or two brake shoes for 3,517,786 Patented June 30, 1970 which there is sufiicient slack, one or more brake shoes are forced back from the wheels by means of wedges and the hand brake is set and released which operates the slack adjuster to let out additional slack to permit ap plication of one or more brake shoes.

The present invention greatly facilitates the replacement of brake shoes because there is always sufficient slack available to permit the renewal of any number of brake shoes without manipulation of the hand brake.

These prior art slack adjusters are of two types, those which take up the incremental slack during the application half of the braking cycle, and those which take it up during the release half, the term incremental referring to 'any slack that would accommodate more than 7% inches of piston movement.

The adjusters of the first type are built with large compression springs to enable the slack adjuster to store the very substantial amount of power that is required to move the heavy body levers, the long body brake rods, and to swing the brake beams and brake shoes up against the wheels. These large springs create a hazard when the adjuster is handled apart from the car, and also when repairs or replacements are made to the body brake rigging. New adjusters are shipped with gags to hold the springs in compressed position. These gags must be carefully removed when the adjuster is applied to the car. Care must be exercised when working on the body brake rigging to prevent accidental release of the adjuster springs.

-My invention eliminates these hazards because it does not have compression springs which remain under compression when the brakes are released. My slack adjuster is safe to ship, to handle, and presents no hazard to anyone working on the body brake rigging.

The second type of slack adjuster measures the slack as the brakes are applied and stores this information until the brakes are released, at which time the adjuster shortens or lengthens in small increments to take up the incremental slack. The disadvantage of this type of operation is that the adjuster adjusts for the next brake application and is not necessarily correct for the instant application. This is disadvantageous if conditions have changed bet-ween the two brake applications, as by change of wheels, or replacement of one brake shoe which does not require hand brake manipulation. Due to these changed conditions the first application of the brake may overbrake the car with the possibility of sliding the wheels fiat, or it may underbrake the car if the changed condition is due to long travel. Conditions do occur in which the hazard of underbraking or overbraking will not be rectified until several brake applications have been made. Therefore to avoid this hazard which is incident to any mechanical change or repair in the brake system, it is necessary that the hand brakes be set and released several times until it appears that the slack adjuster has adjusted itself to accommodate 7 /2 inches of piston travel.

A further defect of this type of operation is that the repair man cannot be depended upon to know which type of slack adjuster has been installed in the car so as to determine whether these additional manipulations of the hand brakes are necessary.

In the standard brake rigging for railway cars, there is a brake mechanism at each end of the car for each truck, and also an air actuated body lever system mounted beneath the middle of the car body for actuating the brake mechanism. The body lever system and the brake mechanism are connected to each other by tension links known as top rods. The body lever system pulls the top rods toward each other 'with a mechanical advantage sufiiciently high to develop the required braking force.

According to my invention I provide an auxiliary lever or other force transmitting system which is actuated by the same piston as the body lever system, for pulling the top rods toward each other with a much less mechanical advantage so that there will be a much greater movement of the brake shoes per inch of piston travel than occurs during operation of the body lever system.

The body lever system includes a dead lever and a live lever, the latter term referring to a lever which does not have a fixed fulcrum. The use of the live lever permits equalization in the transmission of braking force, The live lever and the dead lever are connected by a tension link known as a center rod. Prior art slack adjusters are in the form of a telescopic device which may be substituted either for the center rod, or for one or both of the top rods. The present invention is described with respect to a slack adjuster which is substituted for the center rod, although the principles of my invention are equally applicable to mechanisms which can be substituted for one or both of the top rods.

Other objects, features and advantages will become apparent as the description proceeds.

With reference now to the drawings in which like reference numerals designate like parts:

FIG. 1 is a diagram showing a conventional brake rigging of a freight car without any slack adjuster;

FIG. 2 is an explanatory diagram illustrating certain principles of my invention;

FIG. 3 is a plan view of a preferred embodiment of my invention;

FIG. 4 is a vertical section taken along line 4-4 of FIG. 3;

FIG. 5 is a transverse section taken along lines 5-5 of FIG. 3;

FIG. 6 is a fragmentary perspective view of the take up cable;

FIG. 7 is a transverse section taken along line 7-7 of FIG. 4;

FIG. 8 is a transverse section taken along line 8-8 of FIG. 3;

FIG. 9 is an elevation of the fulcrum bracket taken along the line 99 of FIG. 8; and

FIG. 10 is a section of the overthrow device taken along line 1010 of FIG. 3.

As shown in FIG. 1 the usual unadjusted brake rigring comprises a cylinder 10 and piston rod 11, the cylinder being mounted on a portion of the underframe 12 of a car.

The brake rigging comprises a live lever 13 connected at one end to the piston rod 11 and at the other end to a top rod 14. A center rod 15 extends from an intermediate point of the live lever 13 to a dead lever 16 having a fulcrum at 17. A top rod 18 is connected to the free end of the dead lever 16.

The top rods 14 and 18 are connected to a brake mechanism 19 located at either end of the car, and which are shown diagrammatically in FIG. 1. The brake mechanism includes a brake shoe 20 for cooperation with the car wheels 21.

In operation, as the piston rod 11 is extended, the live lever 13 will be rotated in a counterclockwise direction pulling up on the top rods 14 and 18 to apply the brake shoes 20 to the wheels 21. Although the live lever 13 has no fulcrum, for purposes of illustration it can be assumed that it pivots about an imaginary point 13a. The live lever 13, top rod 14, and center rod 15 constitute a live lever system of high mechanical advantage for developing the braking force. The distance B in FIG. 1 represents the free travel of the piston up to the brake operating point. In the unadjusted system of FIG. 1, 6 or 8 inches of free piston travel is hardly enough to take up the normal half inch shoe clearance due to the high mechanical advantage of the live lever system. Slack due to play in the linkage and wear of the brake shoes must be taken up by other means.

Commercial slack adjusters operate to regulate the effective length of the center rod 15. Thus the parts are brought into a position from which the available free piston travel is sufiicient to move the brake shoes up to the wheels, at which time subsequent piston extension applies braking pressure to the wheels.

The operation of the center rod contracting mechanism according to my invention is best explained by reference to FIG. 2, in which the center rod is made in two halves, 15a and 15b. Portion 15a includes a rack 22 and portion 15b includes a cooperating pawl 23 which is biased into engagement with the rack by a spring 24.

A cable 25 has one end attached to the portion 15b and is trained around a pulley 26 mounted on the dead lever 16, and has its other end attached to a take-up rod 28. The opposite end of the take-up rod 28 is connected to a take-up lever 29 fulcrumed on the underframe at 30. The piston rod 11 actuates the take-up lever 29' through an extension 11a.

The movement of the take-up lever 29 in a clockwise direction as the piston is extended causes the portions 15a and 15b to telescope into each other, thus taking up the slack. Since the lever system 29 has a much lower mechanical advantage than the live lever system 13, 14 and 15, a relatively small amount of piston travel will take up all of the slack in the system. After the slack is taken up, further movement of the live lever 13 in the counterclockwise direction will tend to tension the center rod 15, but the pawl and rack 23-22 prevents any extension of the center rod with the result that a braking force is now applied to the Wheels with the high mechanical advantage afforded by the live lever 13.

Assuming that there is only 12 inches of slack at each end of the car, the proportions of lever 29 in FIG. 2 are such that three or four inches of piston travel will take up the 12 inches of slack at each end of the car, after which the next increment of piston travel is effective in applying the brake.

According to my invention, the slack is returned to the system at the conclusion of the braking operation, with the result that mechanism must be provided to disengage the pawl 23, and the arrangement of FIG. 2 is preferably modified in other respects. It should be noted that an overthrow spring device 31 must be inserted either in rod extension 11a or in the take-up rod 28 to permit continued extension of the piston rod 11 after the slack is taken up.

FIGS. 3 and 4 show a practical embodiment of my invention. The underframe 12 is represented by the center sill, shown in phantom in FIG. 3, since it overlies the mechanism, this overlying relationship being shown in FIG. 8.

In FIGS. 3 and 4-, a control rod 35 is provided to disengage the pawl 23. However, an improved type of operation is obtained if the control rod is also used to prevent engagement of the pawl 23 with the rack 22 until such time as the piston 11 has been extended a predetermined distance. Thus, it is possible to build into the slack adjuster a definite brake operating point, by means of which the braking force may be controlled according to accepted standards.

The center rod portion 15b includes a housing 36 which is divided into two compartments by a partition 37. One compartment receives the rack 22 of center rod portion 15a. The other compartment slidably receives the control rod 35. The pivot 38 for the pawl 23 is mounted in the walls of the housing 36, and the partition 37 is cut away so that the pawl 23 can be extended into engagement with the teeth 39 (FIG. 7) of the rack 22. The pawl 23 is slotted as at '40 and is engaged by a lug 41 on the control rod 35 so as to maintain the pawl normally out of engagement with the rack, thus permitting free sliding movement of the rack 22 within the housing 36.

The control rod 35 is actuated by a sensing lever 42 (FIGS. 3 and 8), which underlies the live lever 13. One

end of the sensing lever 42 is connected to the corresponding end of the live lever 13 by the pin 43 which also connects live lever 13 to the top rod 14. The other end of the sensing lever 42 is loosely received in an opening (FIG. 9) formed in a bracket 44 which is secured, to a suitable part of the underframe 12. Thus the bracket 44 provides a fulcrum for the sensing lever 42 while at the same time not interfering with slight movements of the lever parallel to its longitudinal axis.

The control rod 35 is secured to the sensing lever 42 by a pin 45 which in the arrangement shown underlies the pin 46 when the piston 11 is fully retracted. The pin 46 connects the center rod portion 15b to the live lever 13.

In operation, when the piston 11 is extended to the required distance which represents initial application of braking pressure, in this instance 7 /2 inches, the horizontal separation of pins 45 and 46 is sufficient to cause relative motion of the lug 41 with respect to the housing 36 to an extent sufiicient to disengage the lug 41 from the pawl 23 so that the spring 24 will cause the pawl 23 to engage the teeth 39 of the rack 22. Thus the parts 15a and 15b are locked to each other so that further movement of the piston 11 will cause braking pressure to be applied to the.

wheels 21. However at all extensions of the piston of less than 7 /2 inches, the parts 15a and 15b of the center rod are free to move under the forces developed by the lever system 29.

Thus the braking pressure is not applied until the piston 11 is extended to what might be termed the brake operating point. Since the brake operating point is regulated by standards, the performance of the slack adjuster can never deviate from the standards because the lug 41 is pinned to the control rod 35.

Depending upon the amount of slack taken up, the location of point 43 will vary to the right or to the left of that shown in FIG. 3, causing a corresponding variation in the inclination of the levers 13 and 42. However, such variation will not affect the brake operating point of the system because the relative position of the points 45 and 46, and hence of the lug 41 to the pawl 23 is responsive only to the amount of piston extension.

In the embodiment of FIGS. 3 and 4, two pulleys 50 and 51 are substituted for the single pulley 26 of FIG. 2. The pulley 50 is mounted at the end of the take-up rod 28, and the pulley 51 is mounted on a portion of the underframe 12. The outer end of the cable 25 is secured to the dead lever 16 by a clevis 52, and the inner end to the housing 36 by a suitable bracket 53. This arrangement halves the mechanical advantage thus doubling the takeup capacity as compared to the FIG. 2 arrangement. FIGS. 5 and 6 show the details of the pulley and cable arrangement, and pulley 50 being slightly inclined, as shown in FIG. 6, so that the span 54 of cable 25 will lie in substantially the same plane as the span 55, even though the clevis 52 is offset below this plane.

In both the FIG. 2 and FIG. 3 arrangements, the takeup rod 28, the flexible cable 25, and the center rod portion 15b comprise a tension means which provides a connection between three different elements, the take-up lever 29, the dead lever 16, and the live lever 13. In FIG. 2, the connection between the cable 25 and the dead lever 16 is made by the pulley 26, whereas in FIG. 3, the connection between the cable 25 and the take-up rod 28 is made by the pulley 50.

The overthrow device 31, as shown in FIG. 10, comprises a cylinder 56, a plunger 57, and a compression spring 58 interposed in the piston rod extension 11a in such a manner that even though further movement of the take-up lever 29 is prevented by the take-up of all slack, nevertheless the piston 11 can continue its movement into and beyond the 7 /2 inch brake operating point by compression of the spring 58. The spring 58 needs only to be strong enough to overcome the friction of the various linkages and the weight of the brake shoes it does not absorb any substantial portion of the braking force applied by the piston 11.

As shown in FIG. 10, a clevis 60 is mounted on the cylinder 56 and extends beyond the take-up lever, thus providing a point 61 to which the hand brake chain 62 may be attached. When the brakes are actuated manually by the chain 62, the slack adjuster operates in the same manner as when actuated by the piston 11. The clevis 60' is broken away in FIG. 3 for purpose of clarity.

The essential elements of a live lever system which develops a braking force of high mechanical advantage are a live lever, such as the live lever 13, and two tension links, such as the top rod 14 and the center rod 15, the force being applied to one end of the live lever so that one of the tension links is connected to an intermediate point of the live lever.

According to one aspect of my invention, one of the tension links is rendered inoperative at certain times, that is, incapable of constituting a tension transmitting connection from the live lever to a second lever during movement of the piston up to the brake operating point. Thus, the piston movement can be utilized to actuate the auxiliary force developing mechanism which is proportioned to have a much smaller mechanical advantage, one of an entirely different order of magnitude, to the end tliat the available piston travel will take up all of the s ack.

By making the one tension link telescopic, it can in effect thus be rendered inoperative at certain times, the characteristics being that the auxiliary force developing mechanism includes means for reversing the direction of the force with respect to the direction of the piston movement, such as the cable and pulley arrangements shown in FIGS. 2 and 3.

To summarize the operation which has been previously pointed out in connection with the detailed description of the various parts and subassemblies, as the application of air pressure causes the piston 11 to be extended 5 inches, the ratio of take-up lever 29 is such that it will move the take-up rod 28 seventeen inches to the right. This moves the pulley 50 seventeen inches to the right and hence takes up 34- inches of cable, thus shortening the distance between the intermediate points of the body levers 13 and 16 by 34 inches. Thus the rod portions 151: and 15b are telescoped one into the other so that the center rod is shortened by 34 inches. Using substantially the proportions shown in FIG. 1 for the variousl levers of the brake mechanisms 19 and the dead lever 16, this would result in a total take up of substantially 60 inches of slack, or 30 inchesat each end.

Assuming that this 60 inches represents the entire slack in the system, including shoe clearance, at this point the brake shoes 20 engage the wheels 21. However, the braking pressure will not be applied until the piston travels up to the built-in brake operating point, namely 7 /2 inches in the example shown. Thus during the next 2% inches of piston travel, the spring 58 on the overthrow device 31 compresses 2% inches, the pawl 23 being disengaged from the rack 22 during all of this time. As the piston 11 moves into its 7 /2 inch extension, the live lever 13 moves away from the sensing lever 42, whereas the control rod 35 remains stationary, until such time that the pawl 23 clears the lug 41 and moves into engagement with the rack 22. At this point the two center rod portions are locked to each other, and further movement of the piston 11 rotates the live lever 13 in a counterclockwise direction, further compressing the spring 58, with the result that the braking pressure is applied to the wheels with the high mechanical advantage developed both by the live lever 13 and the various levers of each brake mechanism 19. Since the brake shoes are already in contact with the wheels, the development of this high braking pressure represents onl a very small further extension of the piston, of the order of /2 inch or less.

When the brakes are released and the piston 11 is retracted, as soon as the piston passes through the 7 /2 inch point, the pawl 23 will be disengaged from the rack 22,

and as the piston moves through its -inch position, then the take-up lever 29 will be rotated in the counterclockwise direction, thus releasing the tension on the cable 25, and restoring all the slack to the brake rigging, including the desired shoe clearance, thus assuring that the shoes hang clear of the wheels 21. Suitable means may be provided to prevent withdrawal of the rack 22 from the housing 36 by the weight of the brake shoes.

Although only preferred embodiments of my invention have been described herein, it will be understood that various modifications and changes may be made in the construction shown.

I claim:

1. Brake actuating mechanism for the brake rigging of railway cars comprising a pair of body levers, one of said body levers being a dead lever fulcrumed with respect to the body of said car and the other of said levers being a live lever, a top rod extending from a first end of said live body lever, air actuated piston means connected to a second end of said live lever, a center rod extending from an intermediate point of said live body lever and providing a force transmitting connection with said dead body lever, said live lever, top rod, and center rod constituting a live lever system of high mechanical advantage for developing a braking force, and auxiliary force developing means actuated by the initial extension of said piston means to draw said two body levers toward each other with a mechanical advantage substantially less than that developed by said live lever system in order to take up the slack in said brake rigging.

2. Brake actuating mechanism as claimed in claim 1 in which said center rod is a telescopic center rod, and in which said auxiliary force developing means comprises a take-up lever fulcrumed with respect to said car body, a pulley on said dead body lever, and tension means connecting said take-up lever, said dead body lever and said live body lever, said tension means including a flexible cable trained over said pulley.

3. Brake actuating mechanism as claimed in claim 1 in which said center rod is a telescopic center rod, and in which said auxiliary force developing means comprises a take-up lever fulcrumed with respect to said car body, a pulley mounted with respect to said car body, a take-up rod connected to said take-up lever, a second pulley mounted at the end of said take-up rod, and tension means providing a connection between said take-up lever, said dead body lever and said live body lever, said tension means including said take-up rod, and including a flexible cable connected at one end to said take-up rod and being trained around said two pulleys, and being connected at its other end to said dead lever.

4. A slack adjuster for railroad car brake rigging of the type wherein the brake actuating mechanism comprises a dead lever, a live lever, a pneumatic actuating piston connected to said live lever, and center rod means connecting said dead lever and said live lever whereby the force developed by said piston will be applied to the brake mechanism of each truck through top rods, said slack adjuster comprising a telescopic center rod having a first portion linked to an intermediate point of the dead lever, and a second portion linked to an intermediate point of the live lever, said first and second portions being normally operable for free telescopic movement, means to contract the distance between said intermediate points of said dead lever and said live lever to take up the slack in said brake rigging, thus telescoping said center rod portions, said distance contracting means being actuated by said actuating piston at each operation thereof, means for locking said first and second center rod portions with respect to each other after the take up of slack so that further movement of said piston will cause the application of braking force through said locked telescopic center rod, and overthrow means permitting said further movement of said piston.

5. A slack adjuster as claimed in claim 4 in which said distance contracting means comprises a take-up lever fulcrumed with respect to the body of said car and connected to said actuating piston, means connecting a remote portion of said take-up lever with said second center rod portion, said second lever being a third class lever having a mechanical advantage substantially less than the mechanical advantage provided by the system including said -.live lever whereby a comparatively small travel of said piston will take up said slack.

6. A slack adjuster for railroad car brake rigging of the type wherein the brake actuating mechanism comprises a dead lever, a live lever, a pneumatic actuating piston connected to said live lever, and center rod means connecting said dead lever and said live lever whereby the force developed by said piston will be applied to the brake mechanism of each truck through top rods, said slack. adjuster comprising a telescopic center rod having a first portion linked to an intermediate point of the dead lever, and a second portion linked to an intermediate point of the live lever, said first and second portions being normally operable for free telescopic movement, means to contract the distance between said intermediate points of said dead lever and said live lever to take up the slack in said brake rigging, thus telescoping said center rod portions, said distance contracting means being actuated by said actuating piston at each operation thereof, means for locking said first and second center rod portions with respect to each other when said piston has been extended a predetermined distance so that further movement of said piston beyond said predetermined distance will cause the application of braking force through said locked telescopic center rod, and overthrow means permitting movement of said piston after the take up of slack to permit extension of said piston to said predetermined distance to cause actuation of said locking means, said overthrow means also permitting said further movement of said piston beyond said predetermined distance.

7. A slack adjuster for railroad car brake rigging of the type wherein the brake actuating mechanism comprises a dead lever, a live lever, a pneumatic actuating piston connected to said live lever, and center rod means connecting said dead lever and said live lever whereby the force developed by said piston will be applied to the brake mechanism of each truck through top rods, said slack adjuster comprising a telescopic center rod having a first portion linked to an intermediate point of the dead lever, and a second portion linked to an intermediate point of the live lever, means to contract the distance between said intermediate points of said dead lever and said live lever to take up the slack in said brake rigging, thus telescoping said center rod portions, said distance contracting means being actuated by said actuating piston, means for sensing the extension of said piston to a predetermined distance, means for locking said first and second center rod portions with respect to each other when said piston has been extended a predetermined distance, said locking means comprising a rack mounted on one of said center rod portions and a pawl mounted on the other of said center rod portions, the engagement of said pawl with said rack being controlled by said sensing means, and overthrow means permitting movement of said piston after the take up of slack to permit extension of said piston to said predetermined distance to cause actuation of said locking means, said overthrow means also permitting movement of said piston beyond said predetermined distance so as to cause application of braking force through said locked telescopic center rod.

8. A slack adjuster as claimed in claim 7 in which said sensing means includes a sensing lever extending in the same general direction as said live lever, means povotally connecting one end of said sensing lever to that end of said live lever which is remote from said actuating piston, fulcrum means mounted with respect to said car body engaging the opposite end of said sensing lever, a control rod linked to an intermediate point of said sensing lever, and means on said control rod for engaging said pawl.

9. A slack adjuster as claimed in claim 8 in which said second center rod portion includes a housing, said rack being slidably received within said housing, said pawl being pivotally mounted in said housing for selective engagement with said rack, said control rod being slidably received within said housing and having a portion extending beyond said pawl, and said pawl engaging means comprising a lug mounted on said control rod beyond said pawl for maintaining said pawl out of engagement with said rack except when said sensing lever is angularly displaced from said live lever in excess of a predetermined amount.

10. A slack adjuster for railroad car brake rigging of the type wherein the brake actuating mechanism comprises a dead lever, a live lever, a pneumatic actuating piston connected to said live lever, and center rod means connecting said dead lever and said live lever whereby the force developed by said piston will be applied to the brake mechanism of each truck through top rods, said slack adjuster comprising a telescopic center rod having a first portion linked to an intermediate point of the dead lever, and a second portion linked to an intermediate point of the live lever, means to contract the distance between said intermediate points of said dead lever and said live lever to take up the slack in said brake rigging, thus telescoping said center rod portions, said distance contracting means being actuated by said actuating piston, means for locking said first and second center rod portions with respect to each other when said piston has been extended to a predetermined distance, and overthrow means permitting movement of said piston after the take up of slack to permit extension of said piston to said predetermined distance to cause actuation of said locking means, said overthrow means also permitting movement of said piston beyond said predetermined distance so as to cause application of braking force through said locked telescopic center rod, said distance contracting means including a take-up lever fulcrumed with respect to said car body and extending in the same general direction as said live lever, said actuating piston including a piston rod extension extending between said live lever and said take-up lever, and said overthrow means being interposed in said piston rod extension and including a compression spring for absorbing the overthrow movement of said piston.

11. A slack adjuster as claimed in claim 10 which includes a hand brake chain, and means connecting said hand brake chain to said piston rod extension at a point between said overthrow means and said actuating piston,

12. In a railway car 'brake actuating mechanism having a live lever system including a live lever, a telescopic tension link connected thereto, and air actuated piston means connected to said live lever, a slack adjuster comprising means to contract said telescopic tension link, means to lock said telescopic tension link in a contracted position, said link contracting means including a dead take-up lever actuated by said piston means, control means for actuating said locking means when said piston means is extended a predetermined distance to lock said telescopic tension link in said contracted position, and overthrow means associated with said take-up lever to permit movement of said piston when said telescopic tension link is locked in said contracted position.

13. In a railway car brake actuating mechanism having two actuating levers, one being a live lever, a slack adjuster comprising a telescopic tension link connecting said actuating levers and including a housing, a rack slidably received within said housing, a pawl pivotally mounted in said housing for engagement with said rack, and a control rod slidably mounted in said housing for normally maintaining said pawl out of engagement with said rack, a dead take-up lever, air actuated piston means connected to said live lever and to said take-up lever, cable and pulley means connected at one end to said take-up lever and arranged to draw said two actuating levers toward each other to cause telescopic movement of said tension link, means for actuating said rod to cause said pawl to engage said rack when said piston means is extended a predetermined distance whereby said telescopic tension link is locked in a contracted position, and overthrow means associated with said take-up lever to permit movement of said piston means when said telescopic tension link is locked in said contracted position.

References Cited UNITED STATES PATENTS 2,646,138 7/ 1953 Dorey. 2,646,141 7/ 1953 Dorey. 3,040,844 6/ 1962 Holloway et al. 3,119,470 1/ 1964 Rauglas. 3,156,326 11/1964 Showers.

DUANE A. REGER, Primary Examiner U.S. Cl. X.R. 188--l96 

